The present invention relates to radiation sensing, and more particularly to semiconductor imaging devices based on CMOS pixel sensors.
Various semiconductor detector arrays have been used to detect radiation energy in imaging applications. Charge coupled devices (xe2x80x9cCCDsxe2x80x9d) are one type of widely-used semiconductor detector arrays based on transfer of radiation-induced charge through a series of charge coupling stages. A very high charge transfer efficiency must be maintained in a CCD in order to maintain good signal fidelity. This necessitates a special formation process in manufacturing CCDs. This special formation process prevents CCDs from being easily integrated with on-chip integrated circuits such as complementary-metal-oxide-semiconductor (xe2x80x9cCMOSxe2x80x9d) integrated circuits.
Another type of semiconductor detector arrays is active pixel sensor (xe2x80x9cAPSxe2x80x9d) devices. Each active pixel includes a light sensing element and one or more active transistors within the pixel itself to generate and/or process electrical signals indicative of the amount of charge induced by radiation received by the light sensing element. A single stage of charge couple is needed in APS devices. This eliminates the charge transfer over distances through multiple stages inherent in CCDs. Each APS pixel can be formed by using CMOS process. U.S. Pat. No. 5,471,515 to Fossum et al. and U.S. Pat. No. 5,576,763 to Ackland et al. disclose examples of CMOS APS devices, which are incorporated herein by reference.
A CMOS APS imaging device can be configured to include a CMOS circuit in each active pixel for various on-chip operations and controls, e.g., random access and on-chip signal processing.
The present disclosure provides a CMOS APS device capable of two independent modes of operation: a regular imager mode and a winner-take-all mode. In the regular imager mode, all signals from the active pixels are read out to form an image indicative of an input radiation scene. In the winner-take-all mode, the sensor provides information of the pixel that is xe2x80x9cbrightestxe2x80x9d among all pixels in a frame, i.e., the pixel that produces the highest amount of charge. This can be accomplished additional circuitry located in the periphery of a radiation-sensing array to maintain a desired fill factor.
One embodiment of the present invention includes a CMOS sensor array and a pixel-selecting circuit comprises a signal-receiving circuit connected to receive electrical signals from the sensor array, a signal-processing circuit comparing said electrical signals from different CMOS detectors to select a special CMOS detector, and a memory unit storing a signal value and address of the special pixel. The pixel-selecting circuit is located in the periphery of the sensor array to maintain a high fill factor in the sensor array.